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Dental Evidence for the Diets of Pliopleistocene Hominins

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Dental Evidence for the Diets of Pliopleistocene Hominins YEARBOOK OF PHYSICAL ANTHROPOLOGY 54:47–62 (2011) Dental Evidence for the Diets of Plio-Pleistocene Hominins Peter S. Ungar* Department of Anthropology, University of Arkansas, Fayetteville, AR 72701 KEY WORDS Australopithecus; Paranthropus; Homo; molar; incisor ABSTRACT Diet is fundamental to the interaction vide evidence for the physical properties of the foods to between an organism and its environment, and is there- which a species was adapted. Dental microwear can offer fore an important key to understanding ecology and evo- insights into the properties of foods that an individual lution. It should come as no surprise then that paleoan- ate on a day-to-day basis. Taken together, these lines of thropologists have put a great deal of effort into recon- evidence can offer important insights into early hominin structing the diets of Plio-Pleistocene hominins. Most of food choices and adaptations. New methods of analysis this effort has focused on teeth; these durable parts of and theoretical perspectives are improving our under- the digestive system are usually the most commonly pre- standing of the diets of Australopithecus, Paranthropus, served elements in vertebrate fossil assemblages. In this and early Homo, and promise further progress article, I review much of this work. Tooth size, occlusal long into the future. Yrbk Phys Anthropol 54:47–62, morphology, enamel thickness, and microstructure pro- 2011. VC 2011 Wiley Periodicals, Inc. The role of diet in human evolution is of interest to our knowledge (Ungar, 2007b). Because individuals have paleoanthropologists and laypersons alike. Most peo- different food preferences and access to different resour- ple are introduced to the subject in popular diet ces in different places and at different times, there was books. Atkins (2002) The New Diet Revolution for no single menu for a fossil hominin species, no ‘‘nutri- example, described the early hominin, ‘‘eating the fish tional contents’’ labels for us to decipher. But there are and animals that scampered and swam around him, aspects of diet we can infer. And I am convinced that we and the fruits and vegetables and berries that grew can do better than Begun’s (2004) pessimistic lamenta- nearby.’’ While such assertions offer little insight to tion that, ‘‘while it is frustrating to be unable to describe the target audience of the Yearbook of Physical An- a fossil hominoid’s behavior with sufficient detail to be thropology, The New Diet Revolution sold more than able to distinguish it from an edentate, that is probably 15 million copies. And the chapter on hominin diets as good as it gets.’’ in Sears’ (1995) New York Times #1 best seller The Most research on early hominin diets has focused on Zone has undoubtedly been read by millions more fossil teeth. Teeth are usually the most commonly pre- than even the best-cited academic paper on the same served elements in fossil assemblages, and they are the subject. The basic idea is that many chronic degener- only durable parts of the digestive system that contact ative diseases result from a discordance between our food. Teeth are especially important from an ecological biology and the foods we eat because human evolution perspective, as they are positioned at an interface funda- has not kept pace with changes in diet and other mental to the interaction between vertebrates and their aspects of lifestyle (Eaton and Konner, 1985). While environments. As the early naturalist Georges Cuvier is paleoanthropologists are unlikely to solve obesity and quoted to have said, ‘‘montrez-moi vos dents et je vous other healthcare problems any time soon, it is not dif- dirai qui vous eˆtes.’’ ‘‘Show me your teeth and I will tell ficult to understand public interest in the question, you who you are.’’ ‘‘what did early hominins eat?’’ Teeth offer vertebrate paleontologists many different But what explains interest in hominin diets among lines of evidence for reconstructing diet, both those academics? Brillat-Savarin (1825) wrote nearly two cen- related to species-level adaptations, and traces of actual turies ago, ‘‘dis-moi ce que tu manges, je te dirai qui tu use by individuals in life (see Ungar, 2010 for review). es.’’ ‘‘Tell me what you eat, I will tell you who you are.’’ The size, shape, internal architecture, and microstruc- Diet defines us, not just as individuals, but as a spe- ture of a tooth reflect natural selection for efficient ac- cies. And changing diets are surely an important key to understanding hominin evolution. Our food choices dic- tate our fundamental interactions with the environment Grant sponsors: US National Science Foundation; LSB Leakey and, as Fleagle (1999) has written, diet is ‘‘the single Foundation. most important parameter underlying the behavioral and ecological differences among living primates.’’ *Correspondence to: Peter Ungar, Department of Anthropology, Old Main 330, University of Arkansas, Fayetteville, AR 72701. Reconstructions of diet are therefore crucial to paleoan- E-mail: [email protected] thropology; they hold the potential to yield substantial insights into early hominin ecology and evolution. DOI 10.1002/ajpa.21610 We will likely never get at all the details of hominin Published online in Wiley Online Library paleonutrition; there are intractable, intrinsic limits to (wileyonlinelibrary.com). VC 2011 WILEY PERIODICALS, INC. 48 P.S. UNGAR quisition and processing of foods with specific physical gorillas have a much lower incisor–molar size index, pre- properties. Stable isotopes in a tooth, and use-related sumably reflecting ‘‘a diet low in fruit but high in coarse damage and wear tell us about chemical and structural vegetable matter.’’ These results were consistent with properties of foods eaten by the very animal whose Robinson’s original interpretations, as Australopithecus remains are being studied. In this article, I will review had a similar incisor–molar index to gorillas, and Para- approaches that paleoanthropologists take to recon- nthropus had even smaller incisors and larger molars. structing diets of Plio-Pleistocene hominins using tooth Interestingly, Homo habilis had an incisor–molar index size, shape, structure, and wear (see Lee-Thorp and in the range of chimpanzees and orangutans. Sponheimer, 2006 for a review of tooth chemistry). Soon after, Jolly (1970) developed his seed-eater hy- Academic interest in Plio-Pleistocene hominin diets pothesis based on analogy with the gelada, a large-bod- has grown hand-in-hand with new theoretical perspec- ied, terrestrial savanna dweller with precision grip, rela- tives and methods of analysis over the past couple of tively small incisors, and large molars. He suggested decades. Today we address questions I could not have that Paranthropus dental proportions related to an ad- imagined asking in my first published review of the aptation to consume small, tough seeds. Smaller incisors subject (Ungar, 1992). Were early hominins dietary spe- were attributed to a somatic-budget effect wherein selec- cialists or generalists? How versatile were their pal- tion favors the smallest size consistent with function, ates? Do adaptations reflect selection for favored foods and the Oppenheimer effect, wherein stress limits alveo- or less preferred fallback items? These questions are lus development and room for anterior teeth (see made possible in large part by the development of Jungers 1978). Paranthropus was said to have achieved increasingly sophisticated ways of teasing more and a stable adaptive plateau (his Phase I), whereas Austral- more information from teeth. Each line of evidence can opithecus and Homo had increased incisor–molar size provide important insights as we colligate the genetic ratios, and evolved in to a Phase II omnivorous dietary and nongenetic clues. adaptation. DENTAL ALLOMETRY Incisor allometry Researchers have long considered tooth size an impor- Work on tooth size that has followed has considered tant line of evidence of early hominin diets. The lengths the front and back teeth separately, as ratios of the two and breadths of teeth are easy to measure, species differ cannot tell us whether selection is acting on the incisors, from one another in these measurements, and logic dic- molars, or both. Hylander’s (1975) study on anthropoid tates that these differences should relate to variation in incisors provides a case in point. He found that residuals food acquisition and processing. from a regression line of incisor row width plotted against body mass reflect diet such that frugivorous cer- Early work on incisor–molar size ratios copithecines have relatively larger front teeth than do folivorous colobines (see also Goldstein et al., 1978). Fur- Robinson (1954) noted in his seminal paper on South ther, frugivorous squirrel monkeys, lar gibbons, and African hominin dentitions that ‘‘Australopithecinae’’ in chimpanzees have relatively larger front teeth than do general, and Paranthropus robustus in particular, had more folivorous howlers, siamangs, and gorillas respec- small anterior teeth compared with their cheek teeth. tively. He argued that Paranthropus, with its disparity in size The take-home message is that higher primates feed- between the front and back teeth, flattened premolar ing on large-husked fruits likely benefit from larger inci- and molar occlusal surfaces, and thick mandibular cor- sors to process them, whereas those that feed on smaller pora, was well suited to crushing and grinding vegeta- objects (e.g., berries, leaves) do not. Larger incisors have tion such as shoots and
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